Abstract

Abscission is an important process in the life cycle of a plant. It takes place in predetermined sites called Abscission Zones (AZs). In the previous study of our group, a potential abscission-related gene At1g64405 (G2) was identified of particular interest using a transcriptional analysis. The aim of this study was to characterize this gene in detail.

Expression analysis of G2 was carried out by fusing its promoter with GUS or GFP. Reporter gene expression was detected specifically in floral organ AZ and cortical cells surrounding the sites of lateral roots emergence. Crosses were then carried out between G2:GUS plants and three important abscission mutants: ida, 35S:IDA and bop1/bop2 in order to further investigate the expression pattern of G2. The results, together with the bioinformatics analysis, indicate that G2 is specifically expressed in AZ and is an abscission-related gene, and reveal an inverse correlation between the expression of G2 and IDA. A gene manipulation strategy was then undertaken to generate the ectopically expressed and silenced lines of G2. Overexpression of G2 was achieved by fusing G2 to a 35S promoter whereas the null lines were obtained by an RNAi strategy. 35S:G2 plants displayed unusual root hair morphology while down-regulating G2 generated plants where pollen partially failed to develop. 35S:IDA mutants displayed phenotypes with earlier abscission, extended AZ, and the ectopic secretion of AGPs at the site of organ shedding. Ectopic expression of G2 in 35S:IDA plants partially suppressed these features. A bioinformatics analysis was performed to study G2 protein sequence in order to find out potential functional domains and four motifs were selected that may be important for protein function. The potential role of G2 will be discussed in detail in this thesis.